The present invention relates to a push button switch used for an input unit of an electronic apparatus such as a thin notebook-type personal computer.
A conventional push button switch will be explained with referring to FIG. 14 through FIG. 17.
FIG. 14 is a plan view of the conventional push button switch, FIG. 15 is a sectional view of the switch, FIG. 16 is an apparent perspective view of a link member of the switch, and FIG. 17 is a sectional view of the switch during a pressing operation. Key top 1 made of resin has cylindrical stem 1A on the lower surface of the center of the key top and a pair of engaging parts 1B at both sides on the lower surface. As shown in FIG. 16, resin-made frame 2 having substantially a square U-shape has a pair of parallel arms 2C1, 2C2 which include cylindrical spindles 2A, 2B1 (2B2) at both ends, respectively, and spindle 2A for coupling one end of the arm 2C1 to that of the arm 2C2. Substantially central parts of arms 2C1, 2C2 of frame 2 have cylindrical shafts 2D1, 2D2, respectively. Resin-made frame 3 having substantially a square U-shape similarly has a pair of parallel arms 3C1, 3C2 which include cylindrical spindles 3A, 3B1 (3B2) at both ends, respectively, and spindle 3A for coupling one end of the arm 3C1 to that of the arm 3C2. Substantially central parts of arms 3C1, 3C2 of frame 3 have long holes 3D1, 3D2, respectively. Shafts 2D1, 2D2 of frame 2 are pivotably and slidably supported by long holes 3D1, 3D2 in frame 3. Frames 2, 3 are coupled to each other in an X-shape in side view to form a link member 4. Spindles 2B1, 2B2 and spindles 3B1, 3B2 in the upper parts of link member 4 are pivotably held on respective pairs of engaging parts 1B disposed at both sides on key top 1.
Spindles 2A, 3A in the lower parts of link member 4 are pivotably and slidably held between each pair of engaging recesses 5B disposed at both sides on resin-made case 5 and switch member 6 under the case. Switch member 6 includes a flexible upper sheet, a movable contact on the lower surface of the upper sheet, a lower sheet, a fixed contact on the upper surface of the lower sheet, and a spacer interposed between both sheets. Therefore, the movable contact faces to the fixed contact. The movable contact and fixed contact touch with each other by pressing switch member 6 with projection 7A on a lower surface of the central part of substantially conical dome part 7. Dome part 7 is made of elastic material such as rubber and placed over the upper surface of switch member 6.
Case 5 includes, at the center, guide hole 5A for engaging and supporting stem 1A of key top 1 and dome part 7, and engaging recesses SB at both sides on guide hole 5A. Metal substrate 8 reinforces the lower surface of switch member 6.
An operation of a push button switch having such a structure will be described. When key top 1 has the upper surface pressed down with a finger, link member 4 held by engaging parts 1B pivots on cylindrical spindles 2B1, 2B2 and 3B1, 3B2. Spindles 2A, 3A which are pivotably and slidably held between case 5 and switch member 6 pivot and slide along recesses 5B.
Frames 2, 3 of link member 4 are supported with cylindrical shafts 2D1, 2D2 in the substantially central parts of arm 2C1, 2C2 and long holes 3D1, 3D2 in the substantially central parts of arm 3C1, 3C2, and are interlocked. When key top 1 is pressed and operated, therefore, key top 1 is pressed down with keeping a substantially horizontal attitude as shown in FIG. 17. Key top 1 pushes and bends dome part 7, and thus, projection 7A on the lower surface of dome part 7 presses switch member 6 to turn on the switch to generate a predetermined signal.
When a pressing force applied to key top 1 is subsequently removed, dome part 7 returns to an original shape due to the elastic restoring force and press back link member 4 and key top 1, and thus the original state shown in FIG. 15 is provided.
Although having a good operability, the conventional push button switch includes tall dome part 7 between key top 1 and switch member 6. Additionally, guide hole 5A for positioning dome part 7 and key top 1 makes the switch entirely high and not easily applicable to a recent thin electronic apparatus.
A thin push button switch easily applied to a thin electronic apparatus is provided.
The switch includes the following elements:
(a) A vertically-movable key top including first and second holding parts;
(b) A first frame having a first end pivotably held by the first holding part, and a second end;
(c) A second frame having a first end pivotably and slidably held by the second holding part, and a second end. A substantially central part of the frame is pivotably coupled to the first frame in an X-shape through a coupling part at a substantially central part of the first frame;
(d) A substantially plate-like base including a first support part for pivotably and horizontally-slidably supporting the second end of the first frame, and a second support part for pivotably supporting the second end of the second frame;
(e) An operating spring disposed between the base and the key top, and elastically deformed outward by the second end of the first frame;
(f) A driving spring for elastically contacting with the second end of the first frame from the lower side and for impelling the second end of the first frame inward. The spring has a tapered part pushed by the second end of the first frame; and
(g) A switch member disposed under the driving spring. The member includes switch contacts pressed and operated by the driving spring.
Another push button switch includes the following elements:
(a) A vertically-movable key top including first and second holding parts;
(b) A first frame having a first end pivotably held by the first holding part, and a second end;
(c) A second frame having a first end pivotably and slidably held by the second holding part, and a second end. A substantially central part of the frame is pivotably coupled to the first frame in an X-shape through a coupling part at a substantially central part of the first frame;
(d) A third frame having a first end pivotably held by the first holding part coaxially at the coupling part;
(e) A plate-like base including a first support part for pivotably and horizontally-slidably supporting the second end of the first frame and the second end of the third frame, and a second support part for pivotably supporting the second end of the second frame;
(f) An operating spring disposed between the base and the key top, elastically deformed outward by the second end of the first frame;
(g) A driving spring elastically contacting with the second end of the third frame from the lower side for impelling the second end of the third frame inward. The spring has a tapered part pushed inward by the second end of the third frame; and
(h) A switch member including switch contacts disposed under the driving spring and pressed and operated by the driving spring.
A thin push button switch can be obtained in which a pressing operation force can be adjusted by changing the pressure of the operating spring. The push button switch including a downsized operating spring has a small projected area.